In recent years, slide fasteners are attached to various kinds of flexible clothes, and a fastener tape itself is often required to have flexibility. Therefore, various kinds of knitted fastener tapes which are more flexible than woven fabrics have been developed. In particular, from the viewpoint of flexibility and excellent stability of form, fastener tapes having warp knitting structure are now widely used.
When a fastener stringer is made by knitting a synthetic resin or metallic fastener elements on a fastener tape, or when a fastener stringer is made by swaging and fixing a metallic fastener elements to a fastener tape, a core thread is generally provided in an element attachment portion of the fastener tape in order to improve attachment strength of the fastener elements to the fastener tape. In particular, when a core thread is arranged in the element attachment portion of the fastener tape having the warp knitting structure as described above, the core thread is knitted into the element attachment portion at the same time as knitting of the fastener tape.
As described above, for example, Patent Document 1 and Patent Document 2 disclose inventions relating to fastener tapes having warp knitting structure wherein a core thread is knitted into the element attachment portion.
Patent Document 1 discloses a fastener tape knitted with a single row needle wherein a core thread is knitted into an element attachment portion. This fastener tape is knitted using three kinds of knitting yarns having different structures, i.e., a chain knitting yarn, a tricot knitting yarn, and a single cord knitting yarn, and a core thread is inserted and knitted between both sinker loops of the single cord knitting yarn and the tricot knitting yarn of the element attachment portion.
According to the fastener tape, a textured yarn is used as the single cord knitting yarn, and the tension of the tricot knitting yarn is more than the tension of the single cord knitting yarn. This causes difference of tension between the sinker loop of the tricot knitting yarn and the sinker loop of the single cord knitting yarn, so that the core thread is pressed to the side of the single cord knitting yarn, and the bulging shapes of portions where the core thread is knitted becomes symmetrical on the front surface and the back surface of the fastener tape.
Therefore, when the metallic fastener elements are swaged and attached to the fastener tape, this can prevent the attachment portion of the fastener elements from being displaced from a central portion in a front/back direction of the tape (direction of the thickness of the tape).
Patent Document 2 discloses a fastener tape knitted by a double interlock knitting machine having front row needles and rear row needles and capable of knitting a double structure with the needles. This fastener tape includes a tape main body portion and an element attachment portion in which a core thread is arranged in a central portion in a front/back direction of the tape. The tape main body portion of the fastener tape is knitted by the rear row needles, and the base structure of the tape main body portion includes a chain knitting yarn, a tricot knitting yarn, and a first inserted weft yarn inserted between four wales in a zigzag manner.
On the other hand, the element attachment portion of the fastener tape is knitted as a double structure. In addition, this element attachment portion includes two rows of wales, and a core thread is arranged between the two rows of wales. The knitting structure of the element attachment portion includes a chain knitting yarn knitted in the front and the back of the tape and two second inserted weft yarns inserted between two wales in a zigzag manner and arranged symmetrically on the front and the back of the tape. The core thread is arranged between the two second inserted weft yarns arranged on the front and the back of the tape.
In this kind of element attachment portion in Patent Document 2, the chain knitting yarn is arranged on the front surface side of the tape and the back surface side of the tape of the two rows of wales with the core thread sandwiched therebetween, and the two rows of wales are pulled by two second inserted weft yarns. Therefore, the element attachment portion has a cross section in a substantially rectangular shape as a whole, and the core thread is held at a substantially central portion by the chain knitting yarn arranged on the front surface side of the tape and the back surface side of the tape of each wale and the two second inserted weft yarns inserted between two rows of wales.
Accordingly, when the metallic fastener elements are swaged and attached to the element attachment portion of the fastener tape, a leg portion of the fastener element is deeply engaged with the element attachment portion of which cross section is in substantially rectangular shape, so that the fastener elements can be rigidly attached to a predetermined position. Therefore, the attached fastener elements are less likely to be detached from the element attachment portion, and this effectively prevents the position of the fastener elements from being displaced in the tape length direction of the fastener tape.
By the way, the fastener tape having the knitting structure is generally superior in flexibility, but as compared with, for example, woven fastener tape, the yarn density is smaller, and the strength of the tape is lower. Therefore, the slide fastener structured using the fastener tape of the knitting structure receives sideway pulling force, the fastener tape is partially cut or split.
Further, when a slide fastener is made with the knitted fastener tape, a flange of the slider may slide on and come into contact with the fastener tape when the slider is moved and slid, and therefore, the knitting yarn in the tape region arranged on a region on which the flange of the slider passes is likely to be cut by friction, and there is a drawback in that there is only a low degree of abrasion resistance caused by sliding movement of the slider.
In order to solve the above drawback of the fastener tape having the knitting structure, for example, Patent Document 3 discloses a fastener tape wherein an interval between a first wale arranged at an edge of a tape of an element attachment portion side and a second wale adjacent to the first wale is set at an interval wider than a wale interval of a tape main body portion, and a wale from the second wale to a predetermined wale is closer than the other wales.
In the fastener tape according to Patent Document 3, no core thread is arranged in the element attachment portion like the fastener tape of Patent Document 1 and Patent Document 2, and after the fastener tape is knitted, the fastener stringer is made by sewing a continuous (for example, coil shaped) element row to the element attachment portion including the first and second wales.
Therefore, the fastener tape of Patent Document 3 is basically different from the fastener tapes of Patent Document 1 and Patent Document 2 which makes the fastener stringer by forming the synthetic resin or metallic fastener elements in the element attachment portion and swaging and fixing the metallic fastener elements.
The fastener tape of Patent Document 3 will be explained more specifically. The element attachment portion of the fastener tape is made of the first and second wales, and a chain knitting yarn and an inserted warp yarn are arranged in the first and second wales. Further, in the first wale, a tricot knitting yarn for forming a knitting structure by reciprocally going back and forth to an adjacent fastener tape is arranged, and in the second wale, a tricot knitting yarn for forming a knitting structure by reciprocally going back and forth to the third wale is arranged. On the other hand, a chain knitting yarn, an inserted warp yarn, and a tricot knitting yarn are arranged in each of the third and subsequent wales constituting the tape main body portion of the fastener tape.
In this fastener tape, an inserted weft yarn which is inserted in a zigzag manner between four wales is arranged. In particular, in Patent Document 3, the inserted weft yarn arranged between the first wale and the fourth wale is arranged to be thicker than the inserted weft yarn arranged in the other portions.
In the fastener tape of Patent Document 3 having the knitting structure as described above, the thick inserted weft yarn is arranged between the first wale and the fourth wale, and the tricot knitting yarn is arranged between the first wale and the wale of the adjacent fastener tape. Moreover, in the fastener tape, no tricot knitting yarn is arranged between the first wale and the second wale, and the second wale is configured to be movable to the side of the third wale.
Therefore, in the fastener tape, the interval between the first wale and the second wale is increased to an interval wider than the wale interval of the tape main body portion, and at the same time, the wales between the second wale and the fourth wale are closer than the fourth and subsequent wales.
As described above, the interval between the first wale and the second wale is increased, so that when continuous element rows are sewn and attached to the element attachment portion of the fastener tape using a sewing yarn, the sewing yarn can be stably accommodated within the interval between the first wale and the second wale, and the position of the sewn element row can be prevented from displacing in the width direction of the tape. Further, according to Patent Document 3, the wales between the second wale and the fourth wale are close to each other, so that even when the tape region from the second wale to the fourth wale slides on and comes into contact with the slider, the yarn is not worn off, and the abrasion resistance can be improved.